CN1144491C - Method and system for providing personal base station communication - Google Patents

Abstract

The portable phone (236) can operate as a cordless phone at a low cost while in the micro cell generated by the micro base station (202), or when leaving the micro cell to receive service in the macro cell generated by the macro base station (204) operating on the same frequency , operate flexibly as a cellular phone. When the car phone (222) receiving the service of the macro base station (204) passes by, the micro base station (202) will submerge the signal of the macro base station (204) for the signal of the portable phone (236). The present invention solves this problem. The method is that the micro base station (202) receives, delays and retransmits all signals sent by the macro base station (204) in addition to sending its own signal, and the duty cycle is 50%, that is, the time for receiving and retransmitting Half and half. This delay appears as a resolvable multipath delay to the mobile station (222), which continues to be able to receive signals intended for it.

Description

Method and system for providing personal base station communication

Background of the invention

I. Field of Invention

The present invention relates to wireless communication systems. More particularly, the present invention relates to novel and improved methods and systems for providing personal base station communications within the coverage area of a cellular network base station.

II. DESCRIPTION OF RELATED TECHNOLOGY

As wireless communication systems become more prevalent in society, the demand for a larger number of advanced services is also increasing. In order to meet the capacity demands of wireless communication systems, some techniques for multiple access to limited communication resources have been developed. Code Division Multiple Access (CDMA) modulation techniques are implemented as one of them, facilitating communication in systems where a large number of users exist. Other multiple access techniques such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) are known in the art. However, CDMA spread spectrum modulation techniques have significant advantages over these other multiple access communication system modulation techniques.

US Patent No. 4,901,307 (issued February 13, 1990 and entitled "Spread Spectrum Multiple Access Communication System Using Satellite or Terrestrial Repeaters") discloses the application of CDMA technology to a multiple access communication system. This patent is assigned to the assignee of the present invention and is incorporated herein by reference. US Patent No. 5,103,459 (issued on April 7, 1992, entitled "System and Method for Generating Signal Waveforms in a CDMA Cellular Network Telephone System") further discloses the technology of applying CDMA to a multiple access communication system. This patent is assigned to the assignee of the present invention and is incorporated herein by reference. US Patent No. 5,101,501 (published on March 31, 1992, entitled "Method and System for Providing Soft Handover in CDMA Cellular Network System Communication") also discloses the application of CDMA technology in multiple access communication systems. This patent is assigned to the assignee of the present invention and is incorporated herein by reference.

The teachings of the above patents have been applied to larger wireless communication systems such as cellular telephone systems which in turn interface with the Public Switched Telephone Network (PSTN). In this way, users of user equipment such as cellular telephones can generally send and receive calls from any other communication equipment connected to the PSTN as long as their user equipment is located within the geographical coverage area of any wireless base station belonging to the cellular network system. The coverage areas of these base stations typically extend over several miles. The base stations of these cellular network systems are generally referred to as "macro" base stations, and their corresponding cell sites are referred to as "macro" cell sites.

Because cellular telephony through these macro base stations is more expensive than traditional landline telephony, there is currently no cost savings for anyone who wants to communicate on a cellular phone by using a cellular phone. Therefore, users of cellular telephones generally only use cellular telephones when conventional wired communications such as away from home or office cannot be carried out. Thus, users have to switch their phones when entering or leaving their homes or offices, which is inconvenient.

Prior art radiotelephones have been proposed which operate in a cellular/cordless dual mode in the same handset. These prior art radiotelephones provide cellular service to the PSTN through the macro area of the cellular communication system and cordless telephone service to the PSTN through "micro" base stations such as standard radiotelephone landlines. When the user enters the coverage area of the micro base station, the cellular network/cordless phone dual-mode mobile phone automatically switches between the standard cellular network mode and the cordless phone mode. Therefore, when the user leaves home, he uses his dual-mode handset in cellular network mode and receives cellular network service charges. However, users within the coverage area of a cordless phone landline, usually at home or in the office, can use the dual-mode phone in cordless phone mode without cellular network service charges.

The problem with prior art solutions is that dual-mode telephones generally have to work in two different frequency bands, use two different communication protocols and two modulation schemes, and therefore must contain additional expensive components. For example, these phones typically include separate transmit and receive paths for the cellular network signal and the cordless phone signal, complex switches and dedicated control circuits. These additional components add to the cost, size and weight of prior art dual mode phones.

Accordingly, what is needed is a communication system that provides both cellular network service and local radiotelephony service without adding cost or complexity to user equipment.

Summary of the invention

The present invention is a novel and improved method and system for providing personal base station communications within a "cell" of a cellular network base station. As defined and used in this specification, the term "cell" refers to a geographic area of coverage, while the term "cell" is used to refer to the actual equipment used for communication, ie, one or more base stations. The present invention provides a personal base station working method and system, wherein the forward link of the personal base station (base station to user equipment) has the same frequency allocation as the forward link of the macro base station to which the cellular network communication system belongs. By enabling personal base stations to operate on the same frequency allocation as macro base stations, operators are not required to use additional spectrum to support micro base stations. Operators have a fixed amount of allocated spectrum, and thus face substantial costs if they use all of the existing spectrum to increase cells and keep frequencies off. Operators generally cannot implement other solutions such as obtaining more spectrum. Although the invention is disclosed herein with reference to a CDMA system, it should be understood that the teachings are equally applicable to other wireless communication schemes, whether digital or analog, and regardless of the modulation scheme used.

In the present invention, the first radio base station operates in the same frequency band as the second radio base station. A first radio base station, a "macro" base station, generates and transmits a first forward link data signal and communicates with a first user equipment. A second radio base station, a "micro" base station, generates a second forward link data signal and communicates with a second user equipment. The second wireless base station receives the first forward link data signal, combines it with its own second forward link data signal to form a combined forward link data signal, and then sends the combined forward link data signal to the second wireless base station. data signal. Therefore, the first user equipment communicating with the macro base station can receive and diversity combine the macro base station forward link data from the combined forward link data signal sent by the micro base station, thereby improving the signal-to-noise ratio existing near the micro base station.

In the first embodiment 1 of the present invention, the femto base station combines the first forward link signal and the second forward link signal output by itself at a radio frequency (RF). In the second embodiment of the present invention, the Femto base station combines the first forward link signal and the second front link signal output by itself at an intermediate frequency (IF).

The present invention also delays the received first forward link data signal by a predetermined time delay before combining with the second forward link data signal, so that the signal appears to the first user equipment as a resolvable multipath signal. In order to avoid self-interference, the second radio base station switches the reception of the first forward link data signal and the transmission of the combined forward link data signal at a predetermined switching period. In a preferred embodiment, the predetermined switching period is such that the transmit duty cycle is approximately 50%. Therefore, the micro base station does not transmit continuously substantially, but switches between transmitting the combined signal and receiving the first forward link signal from the macro base station at approximately half of the predetermined time interval.

In another aspect of the invention, the femtocell's power measurer measures the power level of the delayed received first forward link data signal, and the gain adjuster adjusts the delayed received first forward link data signal based on the power level measurement. The power level of the forward link data signal to scale the first forward link data signal relative to the second forward link data signal. In a preferred embodiment, the scaling factor is determined based on the received power of the first forward link signal measured by the power measurer. This scaling is performed to ensure sufficient energy for retransmitting the forward link data of the macro base station in the first user equipment, and avoid excessive degradation of the signal-to-noise ratio of the forward link data of the micro base station itself in the second user equipment.

According to another aspect of the present invention, the second user equipment is handed over to the macro base station by terminating the communication with the second user equipment by the micro base station, or performing handover when the transmission power of the second user equipment exceeds a predetermined threshold, so as to avoid the Inadmissible interference of the 2nd user equipment which is communicating with the macro base station. In this regard, the power control command generator of the femto base station generates power control commands, each command indicating a transmit power increase or decrease. The transmitter of the femto base station sends these power control commands to the second user equipment. In order to avoid excessive interference, if the micro base station sends a predetermined number of consecutive power control commands indicating to increase the transmission power, the micro computer station terminates the communication with the second user equipment. In another embodiment, the base station notifies the second user equipment of the maximum power allowed for transmission by using the micro base station. When the second user equipment communicates with the Femtocell, it is not allowed to exceed this power. When the second user equipment using the micro base station reaches the limited power, the micro base station will continue to send power control commands to allow the second user equipment to increase the transmission power, but the second user equipment will not increase the transmission power. Therefore, the femto base station can detect that the second user equipment is at the edge of its coverage area, and release the call. The micro base station can set the maximum power that the second user equipment is allowed to transmit by monitoring the magnitude of the power received from the macro base station.

According to another aspect of the invention, a macro base station typically includes means for maintaining a very accurate time and frequency reference. This means is typically implemented by a Global Positioning System (GPS) satellite receiver or other expensive equipment. However, providing such accurate equipment at a micro base station would be prohibitively expensive. Therefore, in the present invention, the micro base station obtains accurate time and frequency references from the macro base station. In this regard, the micro base station comprises a demodulator for demodulating the received first forward link, and time reference determining means for determining a time reference from the demodulated received first forward link data signal . In addition, the micro base station further includes frequency reference determining means for determining a frequency reference from the demodulated received first forward link data signal.

Overview of drawings

The features, objects and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings. In the drawings the same reference characters are given the same designation throughout.

FIG. 1 is a curve of received power varying with distance from a macro base station and a micro base station according to the present invention.

Figure 2 is an overall block diagram of the system of the present invention.

FIG. 3 is a block diagram of Embodiment 1 of the micro base station of the present invention.

FIG. 4 is a block diagram of Embodiment 2 of the micro base station of the present invention.

FIG. 5A is an exemplary illustration of the portion of forward link energy transmitted by a macro base station at an arbitrary time interval.

Figure 5B is an exemplary illustration of the combined forward link energy portion of the femtocell transmitted at the same arbitrary time interval as in Figure 5A.

FIG. 6 is a block diagram of an exemplary coding and modulation apparatus for a macro base station.

Detailed Description of Preferred Embodiments

In CDMA cellular systems such as those described in Telecommunications Industry Association (TIA)/Electronics Industry Association (EIA) Interim Standard IS-95, entitled "Mobile Station-Base Station and Macro Standard for Dual-Mode Broadband Spread Spectrum Cellular Network Systems" , the forward link (base station to mobile station) works in the 1.25MHz channel, for example, according to IS-95, the forward link of the base station can work in multiple 1.25MHz wideband CDMA channels located in the range of 869.70MHz to 893.31MHz A specific 1.25MHz CDMA channel.

A CDMA base station can transmit different information signals to each of its user equipment on the same 1.25 MHz channel. A CDMA base station may modulate each information signal with a different pseudo-noise (PN) code, which spreads the information signal. A particular user equipment can then identify the information signal it is interested in by correlating the received signal with the same PN code that the base station used to modulate the signal, thereby despreading only the desired information signal. The other information signals whose PN codes do not match are not despread in the bandwidth. These other information signals thus act as noise in the receiver of the user equipment, representing the inherent interference generated by the CDMA system. For the same reason, signals from neighboring base stations also act as noise in the receiver of the user equipment.

As long as the ratio of the energy per binary bit ( _Eb ) of the desired information signal to the noise power spectral density (No) of the working environment is large enough, the desired information signal can be successfully demodulated. However, when E _b /N _o of the desired information signal is small, such as in the presence of significant interference from other base stations, the error error becomes unacceptably large. Therefore, when the user equipment moves from the coverage area of the first base station to the coverage area of the second base station, and the signal from the second base station exceeds a predetermined threshold, a "handover" from the first base station to the second base station is generally performed. These general principles are described in more detail in the aforementioned patents. Other wireless communication systems apply the same general principles of acceptable signal-to-noise ratios.

Thus, significant problems arise if individual base stations operate on the same 1.25 MHz allocated channel as neighbors of the macro base station. Figure 1 illustrates the problem. Curve 102 represents the power received by the user equipment from the macro base station as a function of distance from the micro base station. Curve 104 represents the power received by a user equipment from a personal base station (also referred to herein as a "micro" base station) as a function of distance from the micro base station. Therefore, when the user equipment communicating within the range of the macro base station moves away from the macro base station to the micro base station, the relative power received from the micro base station increases. For the sake of saving, the personal base station is relatively small, and there is no resource to accept handover from the adjacent macro base station even if handover is desired. Furthermore, if the micro base station has resources for accepting handovers, it is not ideal to operate by accepting all handovers or calls from the macro base station. Thus, at a certain distance denoted "D", the power received from the micro base station representing interference from user equipment communicating with the macro base station becomes large enough to cause an unacceptably high demodulation error rate.

An example of the situation shown in FIG. 1 is when a mobile phone user communicating with a macro base station via a mobile phone in a vehicle drives past a personal base station having a forward link operating on the same assigned frequency as the macro base station forward link. Since the personal base station is owned by the house owner, it is generally arranged to only accept user equipment from "home" (that is, user equipment associated with the micro base station) and not to accept "outside" user equipment (that is, user equipment not associated with the micro base station) call out or switch. This can be achieved, for example, by the femto base station identifying a mobile station identity such as an IMSI or ESN that is allowed to make an outgoing call or handover. To avoid spoofing, the "home" user equipment can be checked by using an authentication key or a personal identification number (PIN) shared by the femto base station. The micro base station can also be notified by the network of authorized mobile stations, so that the micro base station can identify these mobile stations via IMSI or ESN. Therefore, without the present invention, the interference from the personal base station would be unacceptably large when the mobile phone user is close to the house.

I. Micro base station repeater

The present invention provides a working method and device for a personal base station, wherein the forward link of the personal base station is in the same channel as the forward link of the macro base station to which the adjacent wireless communication system belongs. The solution is to have the personal base station "listen" part of the time to the signal that the macro base station sends to the user equipment on its forward link. The micro base station combines the forward link data of the macro base station with the forward link data output by itself. These two signals can be adjusted in proportion to each other and combined, so that the passing user equipment can demodulate the desired information signal sent by the macro base station from the combined signal sent by the micro base station. Figure 2 illustrates an overview of a system 200 of the present invention.

In FIG. 2 , mobile station 222 is shown communicating with macro base station 204 . Accordingly, transceiver (XCVR) 218 transmits information signals desired by mobile station 222 at macro base station antenna 216 and forward link path 226 as part of the macro base station forward link data. Mobile station 222 receives macro base station forward link data through antenna 220 . Mobile station 222 also transmits a reverse link signal via antenna 220 and reverse link path 228 that is captured by macro base station antenna 216 and received by XCVR 218 . Thus, mobile station 222 generally corresponds to an “outsider” user equipment that is not associated with femtocell 202 .

FIG. 2 also shows a portable station 236 in communication with the femto base station 202 . The portable station 236 receives the forward link signal transmitted by the femto base station 202 on the forward link path 232 . Portable station 236 also transmits a reverse link signal on reverse link path 234 , which signal is received by femto base station 202 . Thus, the portable station 236 generally corresponds to the "home" user equipment associated with the micro base station. Portable station 236 can also receive some signals from macro base station 204 on the forward link. However, the present invention assumes that the mobile station does not perform soft handover with the macro base station. Therefore, the macro base station 204 will cause some interference to the portable station 236, so that the portable station 236 cannot obtain the desired signal from the macro base station 204 with the user. Likewise, macro base station 204 may receive some signals from portable station 236, but the station does not process the reverse link from portable station 236, so the receiver's signal is interference.

It is to be noted that both mobile station 222 and portable station 236 may be any type of wireless subscriber equipment, whether vehicular, portable, or otherwise. However, these devices are referred to herein as mobile station 222 and portable station 236 for clarity and brevity of illustration.

Femto base station 202 also receives forward link data signals transmitted by macro base station 204 on forward link path 224 . The signal is captured by femtocell antenna 206 and passed to combiner 214 by duplexer 208 . The combiner 214 combines the forward link data signal sent by the macro base station 204 and the forward link data of the micro base station itself. The resulting combined forward link data signal is then transmitted through duplexer 208 and antenna 206 . Mobile station 222 receives the combined forward link data signal on forward link path 230 . Accordingly, mobile station 222 can receive and diversity combine the macro base station forward link data on forward link path 226 and forward link path 230 , improving the signal-to-noise ratio present in the vicinity of micro base station 202 . Portable station 236 also receives the same combined forward link data signal on forward link path 232 .

The duplexer 208 also provides the function of separating the transmit frequency of the portable station 236 from the transmit frequency of the femto base station 202 . The signal received from portable station 236 is fed to a receiver and demodulator not shown in FIG. The receiver and demodulator are of the same type as used by the macro base station 204 . However, the micro base station 202 is usually designed to handle only one call or a small number of calls, so the receiver and demodulator of the micro base station 202 can be much simpler in design than the receiver and demodulator of the macro base station 204 .

In Embodiment 1 of the present invention, the micro base station 202 combines the forward link signal of the macro base station and the forward link signal output by itself at a radio frequency (RF). Figure 3 illustrates this embodiment 1 of the invention. Femto base station 202 receives macro base station forward link signals on forward link path 224 . Antenna 206 passes the received forward link signal to delay element 304 via duplexer 208 . Delay element 304 introduces a predetermined time delay to the received forward link signal, as discussed in detail below. The delayed forward link signal is passed to scaling unit 320 , which scales the delayed forward link signal by a scaling factor g generated by gain adjustment unit 312 . Scaling unit 320 may contain attenuators, amplifiers, or both, in order to adjust the signal from macro base station 204 to the correct level. The structure of these components is known in the art.

In a preferred embodiment, the duplexer 208 is a switch as shown in FIGS. 3 and 4 . As noted above, a more general duplexer may be combined to allow for antenna 206 to receive transmissions from portable station 236 . In this application, duplexer 208 drops the received transmit signal from portable station 236 and feeds it to receiver 324 . This is known in the art and is not shown in the figures.

In a preferred embodiment, the scaling factor g is determined according to the received power of the forward link signal measured by the power measurer 310 and the gain of the forward link signal of the Femtocell sent by the transmitter (XMTR) 314 . The scaling factor g provides a means for scaling the received macro base station forward link signal relative to the micro base station forward link data signal that has been upconverted and amplified by XMTR 314 . This scaling is performed to ensure that the Eb/No of the forward link data of the macro base station retransmitted at the mobile station 222 is large enough to make the Eb/No of the forward link data of the micro base station itself in the portable station 236 of the micro base station user Do not deteriorate excessively. The scaled macro base station forward link signal is combined in combiner 322 with the micro base station forward link signal generated by XMTR 314 . The resulting combined forward link signal is provided through duplexer 208 to antenna 206 for radiation on forward link paths 230 and 232 .

In Embodiment 2 of the present invention, the micro base station 202 combines the forward link signal of the macro base station and the forward link signal output by itself at an intermediate frequency (IF). Figure 4 illustrates this embodiment 2 of the invention. In Embodiment 2, the micro base station 202 receives the macro base station forward link signal on the forward link path 224 . Antenna 206 passes the received forward link signal to receiver 403 through duplexer 208, which downconverts the signal to IF. Then, the IF macro base station forward link signal is transmitted to the delay element 304, introducing a predetermined time delay. The delayed forward link signal of the IF macro base station is sent to the scaling unit 320 , and the delayed forward link signal is scaled according to the scaling factor g generated by the gain adjusting unit 312 . In a preferred embodiment, the scaling factor g is determined according to the received power of the forward link signal measured by the power measurer 310 and the gain of the preamplifier 415 for amplifying the forward link signal of the IF micro base station. The scaling factor g provides a means for scaling the IF macro base station forward link signal relative to the IF micro base station forward link data signal amplified by preamplifier 415 . The scaled IF macro base station forward link signal is combined with the IF micro base station forward link signal in combiner 322 . The resulting combined forward link signal is provided to transmitter 414 which is upconverted and amplified for transmission and radiated at antenna 206 through a duplexer onto forward link paths 230 and 232 .

As a result, the forward link transmit power of macro base station 204 varies according to curve 106 in FIG. 1 . Specifically, the forward link effective power density of the macro base station 204 (or the power received by the mobile station 222) varies according to curve 106, which is very close to the curve 102 when only the macro base station 204 radiates, until the mobile station 222 Close to the micro base station 202 . At this proximity, the mobile station 222 is able to receive both the micro base station 202 and the macro base station 204 , thus somewhat beyond curve 102 . If the mobile station is very close to the micro base station 202, then basically only the power of the micro base station 202, and thus varies according to the curve 104.

Since the forward link of the macro base station 204 is on the same frequency assignment as the forward link of the micro base station 202, what compromises the invention is that the micro base station 202 does not "listen" to the macro base station 204, but transmits itself. Obviously, this would cause unacceptable inherent interference. Accordingly, the present invention provides a timing scheme that avoids this inherent interference.

5A and 5B illustrate the timing scheme of the present invention. FIG. 5A is a diagram of the forward link energy of a macro base station over a period of time. In this exemplary illustration, the forward link of the macro base station is illustrated for the period T ₀ -T ₅ . The data for time periods T ₀ -T ₅ are denoted as C ₁ -C ₃ , respectively, in FIG. 5A . It can be seen from FIG. 5A that the macro base station can continuously transmit data during the time period T ₀ -T ₅ , which is roughly the same as that performed by the system conforming to the IS-95 standard. Thus, FIG. 5A represents a macro base station forward link signal routine over the time period observed on forward link path 224 of FIGS. 2, 3 and 4. FIG.

FIG. 5B is a forward link energy diagram of a micro base station during the same time period as FIG. 5A . The shaded portion of the time period indicates that the femto base station 202 is not transmitting, but is "listening" to the macro base station forward link signal as shown in FIG. 5A. The unshaded part indicates that the micro base station 202 is sending a combined signal including the forward link data of the micro base station and the macro base station. It can be seen from FIG. 5B that the micro base station 202 does not substantially transmit continuously during the time period T ₀ -T ₅ , but switches between sending combined signals and receiving macro base station forward link signals roughly at half intervals of each time period. . In a preferred embodiment, a short guard period is also provided, during which the Femto base station does not send combined signals nor receive macro base station forward link signals. In FIG. 5B, the guard period is represented by a short blank period between consecutive shaded blocks and unshaded blocks. Thus, FIG. 5B represents a general example of a femto base station combining forward link signals over the time period observed by forward link paths 230 and 232 of FIGS. 2 , 3 and 4 .

In the preferred embodiment, the timing scheme of FIG. 5B is accomplished by delay element 304 and the switching devices of duplexer 208 . Additionally, receiver 324 (FIG. 3) or 403 (FIG. 4) and transmitter 314 (FIG. 3) or 414 (FIG. 4), respectively, may implement switching means by alternately masking transmit and receive signals. In a preferred embodiment, at the time represented by the shaded time period in FIG. 5B , duplexer 208 transmits the input macro base station forward link signal to delay element 304 and receivers 324 ( FIG. 3 ) and 403 ( FIG. 4). Thus, the micro base station "listens" to the first half of the forward link data periods _C1 - _C5 of each macro base station in FIG. 5A. As described above, delay element 304 introduces a predetermined delay to received macro base station forward link signals. This predetermined time delay is equal to the switching period, ie half a time period. During the time period represented by the unshaded portion in FIG. 5 , duplexer 208 passes the output combined forward link signal to antenna 206 for radiation on forward link paths 230 and 232 . Therefore, the combined signal sent by the Femtocell represented by the unshaded part in FIG. 5B includes the forward link data from the Macrobase station in the last half time period.

Since the micro base station 202 cannot "listen" to the forward link of the macro base station 204 when it transmits by itself, the base station essentially "misses" half of the data transmitted by the macro base station 204 on the forward link. That is to say, delay and retransmission cannot be performed on the second half of each macro base station 204 forward link data period C ₁ -C ₅ . Therefore, the period of the handoff interval is preferably selected such that "missing" data has the least effect on the combined forward link signal demodulation and decoding capabilities of mobile station 222 or portable station 236 . Determining an acceptable handover period largely depends on the design of the forward link used by the macro base station 204 and the micro base station 202 on their respective forward links.

An example of a forward link coding and modulation scheme for the forward traffic channel of macro base station 204 or micro base station 202, which is based on IS-95, is illustrated in FIG. It should be noted that other communication channels such as pilot and synchronization channels can be coded and modulated in the same manner. However, for clarity and brevity, the operation of traffic channels is discussed here.

In FIG. 6, the multiplexed and framed forward link information data is provided to convolutional encoder 602. In FIG. In the exemplary embodiment, the rate of the convolutional code is 1/2, so that the input encoder 602 produces 2 symbols per data bit. Also in the exemplary embodiment, encoder 602 has a constraint length of nine. As is well known in the art, convolutional coding involves a modulo-2 sum of selected branches in a serially delayed input data sequence. The delay length of the data sequence is equal to K-1, where K is the constraint length. Therefore, the output of convolutional encoder 602 is twice the input rate, and each resulting convolutionally encoded modulation symbol depends on other adjacent modulation symbols according to the constraint length. Obviously, other code ratios and constraint lengths can be used.

The output of convolutional encoder 602 is provided to symbol repeater 604 . In an exemplary embodiment, the symbol repeater 604 repeats each convolutionally coded modulation symbol according to the information data rate, so as to obtain an output with a constant modulation symbol rate. For example, if the information data rate is the highest 9600bps, the symbols are not repeated. The information data rate is half of the highest rate (or 4800bps), and each symbol is repeated once (each symbol appears twice consecutively). When the information data rate is a quarter of the highest rate (or 2400bps), each symbol repeats 3 times. When the information data rate is one-eighth of the highest rate (or 1200bps), each symbol repeats 7 times. It can be seen that the result of this example achieves a constant modulation symbol rate at which the symbol repeater 604 outputs 19200 modulation symbols per second. Obviously, other rate sets can be used.

The output symbols of symbol repeater 604 are provided to block interleaver 606 . In the exemplary embodiment of the traffic channel, the interleaver spans 20 ms, equivalent to 384 modulation symbols at an exemplary modulation symbol rate of 19200 symbols per second. The interleaver array is 24 rows x 16 columns. Symbols are written into the array of block interleaver 606 in columns and read out in a pattern with a large dispersion of adjacent modulation symbols.

In the forward traffic channel example, the interleaved modulation symbols read from block interleaver 606 are input to modulo 2 adder 608 and masked with the long code PN assigned to mobile station 222 . After the long code generator 614 generates a PN sequence with a rate of 1.228Mcps, it is down-sampled to 19200Ksps by the decimator 616, so as to match the modulation symbol rate. The PN sequence is further down-sampled by decimator 618 to mask or randomize the position of the power control bits interleaved by multiplexer (MUX) 610 to the forward traffic channel.

Then, in the modulo 2 adder 612, the forward traffic data is orthogonally spread relative to other forward channels by using the assigned traffic channel Walsh function with a fixed chip rate of 1.2288 Mcpc. Again, after the forward traffic data are respectively orthogonally spread by the I channel and the Q channel PN spreading sequence PN _I and PN _Q , the modulo 2 channel data is filtered in the filters 624 and 626 respectively, and the mixer 628 and 630 up-converts to carrier frequency fc. The resulting I and Q channel RF signals are combined in combiner 632, the output of which is further power amplified and radiated on antenna 216 (see FIG. 2). The exemplary coding and modulation scheme of FIG. 6 is described in more detail in the aforementioned US Patent No. 5,103,459.

The exemplary coded modulation scheme described above is very robust and error proof. As a result, the length of the "listen" time is slightly less than about a 50% duty cycle without significant data loss. Therefore, the variable range of the switching period used in the present invention in the communication system adopting the above-mentioned strong-function error-proof coding scheme is larger than the range used in the scheme system that must adopt the low-function scheme due to the narrow frequency band. For example, in the exemplary embodiment described above, each information bit is encoded by the rate 1/2 convolutional encoder 602 . Therefore, there are at least 2 modulation symbols per bit, and lower rates have more redundant bits added by the symbol repeater 604 . Adjacent modulation symbols are temporally dispersed by the block interleaver 606 . In addition, the constraint length of the convolutional encoder 602 and the uniqueness of the symbols used both increase the robustness of the encoding scheme. Therefore, assuming that the transmitted signal energy is sufficient, the switching period can be on the order of milliseconds without significant data loss. Assuming that the frame length is 20ms, the switching period can be close to 10ms. In addition, the switching period can be as short as the duration of one modulation symbol. At this time, every other symbol is lost. In another embodiment, the switching period can be as short as the duration of one PN chip. In yet another embodiment, the switching period can be randomized. Determining an acceptable handover period depends largely on the forward link design used by macro base station 204 and micro base station 202 on their respective forward links. In the example of a system conforming to the IS-95 standard, the period T _i+1 -T _i would be long enough to cause a delay of more than one PN spreading chip (separating the multipath signals generated by the micro base station 202 by at least one chip), Thus, the transmitted spectrum is the spectrum of the original IS-95 signal. However, the period T _i+1 -T _i should not be so long that the mobile station 222 cannot track the phase and timing of the base stations. The IS-95 system appears to further consider the orthogonal forward links separated by the Walsh function. Orthogonality suffers somewhat when the mobile receives only part of the Walsh function, and the required signal-to-noise ratio increases due to coupling between the forward link Walsh channels. To maintain orthogonality, switching may be performed per Walsh function or an appropriate multiple of the time span of each Walsh function. In the case of the IS-95 system, the positions of the power control bits are randomized for clarity and multiplexed into the data stream, as shown in Figure 6. These power control bits occupy 1 or 2 Walsh functions every 1.25ms on the forward link. For IS-95 systems, the handoff times can be randomized so that mobile stations 222 receiving to macro base station 204 receive all power control bits. The proper switching duration and the selection of the proper switching time depend on the items mentioned above as well as the complexity of the delay element 304, among other things.

It should be noted that mobile station 222 (see FIG. 2 ), which is in communication with macro base station 204 , continues to transmit reverse link data to macro base station 204 on reverse link path 228 . While mobile station 222 is receiving the combined forward link signal from femto base station 202 on femto base station forward link path 230, femto base station 202 cannot demodulate the signal from mobile station 222, although the signal is strong enough for demodulation. In other words, mobile station 222 does not perform a handover to femto base station 202 even though the pilot signal strength of femto base station 202 exceeds the nominal handoff threshold, as discussed in the aforementioned US Patent No. 5,101,501.

To mobile station 222, the combined forward link signal received from micro base station 202 on forward link path 230 appears very similar to any multipath component transmitted by macro base station 204, except that it is "truncated" for half the time period. state. Thus, mobile station 222 capable of diversity combining multipath signals in the preferred embodiment is sufficiently assisted by the additional energy provided by forward link path 230 to avoid unacceptably high demodulation error rates. In addition, adding some "outside" mobile stations 222 will not increase the load on the micro base station 202 because the micro base station 202 retransmits whatever it receives on the specific frequency allocation (ie, the entire macro base station forward link).

In many cases, the micro base station 202 is within the coverage area of a macro base station 204 . At this time, the micro base station only retransmits the forward link of the macro base station 204 . However, U.S. Patent No. 5,101,501 (published on March 31, 1992, entitled "Method and System for Providing Soft Handover in CDMA Cellular Network System Communication") discloses that all CDMA base stations transmit at the same frequency, so that mobile stations can use soft handover . In this case, the femto base station 202 retransmits the signals of those base stations it was receiving with a power proportional to the strength of the signal received by the femto base station 202 .

II. Time and Frequency References

According to another aspect of the present invention, the micro base station 202 demodulates at least one logical channel of the macro base station 204 forward link signal to obtain a stable time and frequency reference. As explained above, macro base station 204 typically includes means for maintaining a very precise time and frequency reference. This reference is typically accomplished using a Global Positioning System (GPS) satellite receiver (not shown) or other expensive equipment. However, providing such accurate equipment at femto base station 202 would be prohibitively expensive. Therefore, in the present invention, the micro base station 202 obtains an accurate time and frequency reference from the macro base station 204 .

Referring back to FIG. 3 , antenna 206 captures the macro base station forward link signal from forward link path 224 and passes the signal to receiver (RCVR) 324 through duplexer 208 . Receiver 324 downconverts the RF signal and passes it to demodulator (DEMOD) 326 . Demodulator 326 searches, acquires, and demodulates the pilot channel sent as the macro base station forward link signal. In an exemplary CDMA system, this pilot signal can be used to achieve initial system synchronization and provide robust time frequency and phase tracking of the macro base station forward link signal. In this exemplary CDMA system, each base station also transmits a synchronization channel that uses the same PN sequence and PN phase as the pilot channel, which can be demodulated whenever the pilot channel is tracked. This synchronization channel carries information including the macro base station 204 identity and the exact macro base station 204 pilot PN carrier phase offset.

The synchronization information is passed from demodulator 326 to time and frequency unit (TFU) 330 . Thus, TFU 330 can determine accurate system time and obtain a stable frequency reference from macro base station 204 . TFU 330 then provides this timing and frequency information to transmitter 314 and receiver 324; and to duplexer 208 if duplexer 208 is performing a switching function. In the case of the IS-95 system, the micro base station 202 may not need to demodulate the synchronization channel of the macro base station 204 to obtain the marker and pilot code PN carrier phase offset of the macro base station. This is because the micro base station 202 does not move and this information is static. Accordingly, the information may be provided to the micro base station 202 by means such as means of the micro base station 202 .

The same teaching as above may also be used for the embodiment of FIG. 4 with respect to receiver 403 and transmitter 414 . The micro base station 202 may then continuously track the macro base station pilot channel, or "coast" for a predetermined period of time, and only obtain periodic updates to the system time and frequency reference.

It should be noted that the time and frequency reference aspects of the invention are described here with reference to an exemplary CDMA system, but that the teachings of the invention are equally applicable to other communication systems, whether digital or analog, and are independent of the modulation or channelization scheme used. For example, the present invention can also be used in a communication system in which the pilot channel of the macro base station itself has a system time reference. Furthermore, the pilot channel may not be on the same carrier frequency or time slot as any other forward link channel. The present invention is not intended to be limited to the specific embodiments described herein, as one of ordinary skill in the art can apply the teachings of the present invention to a wide variety of communication systems.

III. Micro base station power control

According to another aspect of the present invention, the femto base station 202 controls the reverse link power level of the portable station 236 to avoid undue interference with reverse link signals received by the macro base station 204 from other UEs such as the mobile station 222 . As is well known in the art, the wireless communication system 200 may use a combination of open-loop and closed-loop power control methods to maximize capacity and prevent user equipment from interfering too much with each other. In the open-loop power control method, the consumer device measures the transmitted power when it receives the pilot signal. Then, the user equipment responds by adjusting its transmit power inversely, that is, the weaker the received signal is, the stronger the transmitter power of the user equipment is. In the closed-loop power control method, the cell station sends a power adjustment command to the user equipment, so that it increases or decreases the power of the transmitter by a predetermined amount according to the plan. US Patent No. 5,056,109 (issued October 8, 1991, entitled "Method and Apparatus for Controlling Transmission Power in a CDMA Cellular Mobile Telephone System") discloses such a power control system and method. This patent is assigned to the assignee of the present invention and is incorporated herein by reference.

In the above-mentioned patent, a combination of open-loop and closed-loop power control is used to adjust the transmit power of all mobile stations 222 communicating with the macro base station 204 so that they reach the macro base station 204 at approximately the same predetermined power level. The same power control technique can be used to control the transmit power of all portable stations 236 that are communicating with the micro base station 202 so that these portable stations arrive at the micro base station 202 at approximately the same predetermined power level. However, the portable station 236 generally does not communicate with the macro base station 204 as long as communication with the micro base station 202 is satisfied (to avoid incurring cellular network system access fees). Therefore, macro base station 204 cannot use closed loop power control commands to instruct portable station 236 to "turn down" its transmit power. As shown in FIG. 2, when the portable station 236 is far away from the micro base station 202, the received power obtained from the micro base station 202 is weak. As a result of both open loop and closed loop power control, a portable station 236 that is communicating with the microcell 202 transmits as much power as is sufficient for the microcell 202 to receive. As a result, portable station 236 continues to increase its power level as it moves farther away from femtocell 202 , causing unacceptable interference on reverse link path 228 .

In the present invention, no matter whether the micro base station 202 terminates the communication with the portable station 236, or performs handover when the transmission power of the portable station 236 exceeds a predetermined threshold, and switches the portable station 236 to the macro base station 204, the above-mentioned unacceptable situation can be avoided. interference. In Embodiment 1, the femto base station 202 itself decides when the transmission power of the mobile station 236 may be too high.

In the first embodiment, FIG. 3 or FIG. 4 can be applied, the antenna 206 receives the reverse link signal from the portable station 236, and transmits the signal to the receiver 324 (FIG. 3) or the receiver 403 (FIG. 4). Receiver 324 or 403 downconverts the received reverse link signal to demodulator 326 as discussed above. Power control command generator 332 measures the average power of the reverse link signal transmitted by portable station 236 after demodulation and compares the average power to a desired threshold to generate A "raise" or "lower" command is sent to portable station 236 via transmitter 314 (FIG. 3) or 414 (FIG. 4).

Intuitively, when the portable station 236 leaves the Femtocell, the average reverse link signal power measured by the power control command generator 332 decreases due to path loss. Power control command generator 332 responds by sending portable station 236 a series of "boost" commands. In this Embodiment 1, the power control command generator 332 keeps track of how often a "boost" command is required to be sent to the portable station 236 . If the corresponding portable station 236 must transmit with a higher power level in order to provide a sufficient reverse link signal on the reverse link path 234, more than a predetermined number of "boosts" are sent in the power control command sequence. " command, then the micro base station 202 terminates the communication with the portable station 236, or executes the handover of the portable station 236 to the macro base station 204. For example, if the femto base station sends K power "up" commands in a set of N power control commands, the femto base station can determine that the personal user equipment exceeds the desired range.

In Embodiment 2, when the mobile station 236 communicates with the micro base station 202, its transmission power is limited to a predetermined maximum level. This can be accomplished using predetermined rules in the programming of the portable station 236 to limit the transmit power of the portable station to a predetermined maximum level during its use of the micro base station 202 . It should be noted that the above limitations are not enforced when the portable station 236 communicates with the macro base station 204 .

Those skilled in the art can conveniently realize the above-mentioned power limitation, for example, by modifying the content taught in the above-mentioned reference document No. 5,056,109, once the portable station 236 communicates with the micro base station 202, its transmission power exceeds the predetermined maximum level, That is, the "up" command is ignored. U.S. Patent No. 5,452,473 (issued September 19, 1995 and entitled "Reverse Link, Transmit Power Correction and Limiting in a Radiotelephone System") discloses a method for the portable station 236 to ignore "upgrade" after the transmit power exceeds a predetermined threshold. A circuit designed for high" command. This patent is assigned to the assignee of the present invention and is incorporated herein by reference. In this embodiment, femto base station 202 can sense that portable station 236 is at the edge of cell coverage by noticing that portable station 236 has disobeyed a series of "raise" commands. Then, the femto base station 202 releases the call. However, when the portable station 236 communicates with the macro base station 204, conventional maximum power levels may be used.

The power limitation of the portable station 236 can also be implemented by a command from the femto base station 202 instructing the portable station 236 to limit its transmit power to a maximum level. The micro base station 202 can determine the maximum level by monitoring the magnitude of the power received from the macro base station 204 with the power measuring device 310 shown in FIG. 3 and FIG. 4 . The greater the power received from the macro base station 204, the greater the maximum allowable transmit power of the mobile station 236 without causing undue interference to other mobile stations operating in the macro base station 204 cell.

Additionally, the portable station 236 can notify the femto base station 202 with a signaling message indicating that the base station has reached its limited power or power threshold. Along with this signaling message, the portable station 236 can indicate the pilot strength of surrounding base stations in the same way as the existing IS-95 pilot strength measurement message, and is further described in the aforementioned US Patent No. 5,101,501. This enables the micro base station 202 to determine whether the portable station 236 is handed over to the macro base station 204 or not.

The above descriptions of the preferred embodiments are provided to enable anyone skilled in the art to make or use the present invention. Various modifications of the above-described embodiments will be readily apparent to those persons, and the general principles set forth herein may be applied to other embodiments without inventive ability. Thus, the present invention is not limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (32)

1. wireless base station and the 2nd wireless base station are in the method for same frequency band work, described the 1st wireless base station produces and sends the 1st forward link data signal, and with the 1st communications of user equipment, described the 2nd wireless base station produces the 2nd forward link data signal, and with the 2nd communications of user equipment, it is characterized in that, comprise following steps:

A. receive described the 1st forward link data signal in described the 2nd wireless base station;

B. make up the 1st forward link data signal and described the 2nd forward link data signal of described reception in described the 2nd wireless base station, form the forward link data signal of combination;

C. send the forward link data signal of described combination from described the 2nd wireless base station,

Described the 1st subscriber equipment receives the forward link data signal from the described combination of the 2nd wireless base station, and diversity makes up the forward link data signal and described the 1st forward link data signal of described combination.

2. the method for claim 1 is characterized in that, also comprises the step that the 1st forward link data signal that makes described reception postpones one period time of delay.

3. method as claimed in claim 2 is characterized in that, also comprises by switching cycle in the described step that receives described the 1st forward link data signal with send the step of switching between the step of forward link data signal of described combination.

4. method as claimed in claim 3 is characterized in that, the described switch step that switches was carried out with 50% duty cycle.

5. method as claimed in claim 3 is characterized in that, continues to be longer than a PN expansion chip described time of delay.

6. method as claimed in claim 3 is characterized in that described switch step occurs over just the walsh function border.

7. method as claimed in claim 3 is characterized in that described switching cycle has the duration at random.

8. method as claimed in claim 3 is characterized in that, also comprises following steps:

A. measure the power level of the 1st forward link data signal of described delay reception;

B. described measuring process is responded, regulate the described power level of the 1st forward link data signal of described delay reception.

9. method as claimed in claim 3 is characterized in that, also comprises following steps:

A. to described the 2nd subscriber equipment transmission power control commands, each described power control command indication transmitted power increases or reduces;

If b. described the 2nd base station sends the predetermined number of consecutive power control command, indication increases transmitted power, just stops and the communicating by letter of described the 2nd subscriber equipment.

10. method as claimed in claim 3 is characterized in that, also comprises following steps:

A. to described the 2nd subscriber equipment transmission power control commands, each described power control command indication transmitted power increases or reduces;

If b. described the 2nd base station sends the predetermined number of consecutive power control command, the indication transmitted power increases, and then carries out handover, and described the 2nd subscriber equipment is switched to described the 1st base station.

11. method as claimed in claim 3, it is characterized in that, when also comprising described the 2nd subscriber equipment and described the 2nd base station and communicating transmitted power is restricted to the step of predetermined maximum level, described predetermined maximum level is lower than conventional maximum level used when communicating with described the 1st base station.

12. method as claimed in claim 11 is characterized in that, also comprises the step that described the 2nd subscriber equipment of described the 2nd base station commands is restricted to transmitted power described predetermined maximum level.

13. method as claimed in claim 11 is characterized in that, also comprises described the 2nd subscriber equipment described the 2nd base station is sent signaling message, indicates the step that the 2nd subscriber equipment is sending with described predetermined maximum level.

14. method as claimed in claim 3 is characterized in that, also comprises following steps:

A. in described the 2nd base station the 1st forward link data signal of described reception is carried out demodulation;

B. the 1st forward link data signal from described demodulated received determines time reference.

15 methods as claimed in claim 3 is characterized in that, also comprise following steps:

A. in described the 2nd base station the 1st forward link data signal of described reception is carried out demodulation;

B. the 1st forward link data signal from described demodulated received determines frequency reference.

16. the system that personal base station work is provided in the wireless communication system area of coverage is characterized in that, this system comprises:

A. the 1st wireless base station, be used for predetermined frequency band produce and send the 1st forward link data signal and with the 1st communications of user equipment;

B. the 2nd wireless base station, be used to produce the 2nd forward link data signal and with the 2nd communications of user equipment; Described the 2nd wireless base station comprises:

1) receiver is used to receive described the 1st forward link data signal;

2) combiner is used to make up the 1st forward link data signal and described the 2nd forward link data signal of described reception, forms the forward link data signal of combination;

3) transmitter is used for sending at described predetermined frequency band the forward link data signal of described combination.

17. system as claimed in claim 16 is characterized in that, also comprises the delay element that the 1st forward link data signal that makes described reception postpones one period time of delay.

18. system as claimed in claim 17 is characterized in that, also comprises the switching device that switches between described receiver and described transmitter by switching cycle.

19. system as claimed in claim 18 is characterized in that, described switching device switched between described receiver and described transmitter with 50% duty cycle.

20. system as claimed in claim 18 is characterized in that, continues to be longer than a PN expansion chip described time of delay.

21. system as claimed in claim 18 is characterized in that, described switching device only carries out the switching between described receiver and the described transmitter on the walsh function border.

22. system as claimed in claim 18 is characterized in that, described switching cycle has the duration at random.

23. system as claimed in claim 18 is characterized in that, also comprises:

A. power checker is used to measure the power level of the 1st forward link data signal of described reception;

B. fader is used to regulate the described power level of the 1st forward link level measurement of described reception.

24. system as claimed in claim 18 is characterized in that, also comprises the power control command transmitting that produces power control command and gives birth to device, each described power control command indication transmitted power increases or reduces; If described the 2nd base station sends K power control command in one group of N power control command, the indication transmitted power increases, and the termination of then described the 2nd base station is communicated by letter with described the 2nd subscriber equipment, and wherein K is the predetermined number less than N.

25. system as claimed in claim 18 is characterized in that, also comprises the power control command transmitting that produces power control command and gives birth to device, each described power control command indication transmitted power increases and reduces; If described the 2nd base station sends the predetermined number of consecutive power control command, the indication transmitted power increases, and handover is carried out in then described the 2nd base station, and described the 2nd subscriber equipment is switched to described the 1st base station.

26. system as claimed in claim 18, it is characterized in that, when described the 2nd subscriber equipment and described the 2nd base station communicate, its transmitted power is restricted to predetermined maximum level, described predetermined maximum level is lower than conventional maximum level used when communicating with described the 1st base station.

27. system as claimed in claim 26 is characterized in that, described the 2nd subscriber equipment of described the 2nd base station commands is restricted to described predetermined maximum level with transmitted power.

28. system as claimed in claim 26 is characterized in that, described the 2nd subscriber equipment sends signaling message to described the 2nd base station, indicates described the 2nd subscriber equipment and sends with described predetermined maximum level.

29. system as claimed in claim 18 is characterized in that, also comprises:

A. demodulator is used for the 1st forward link data signal of described reception is carried out demodulation;

B. time reference determination device, be used for from described demodulated received to the 1st forward link data signal decision time reference.

30. system as claimed in claim 18 is characterized in that, also comprises:

A. demodulator is used for the data-signal of described reception is carried out demodulation;

B. frequency reference determination device, be used for from described demodulated received to link data signal deciding frequency reference.

31. system as claimed in claim 18 is characterized in that, described the 2nd subscriber equipment of described the 2nd base station commands has a thresholding, when is used to detect the power output of this subscriber equipment above this thresholding.

32. system as claimed in claim 31 is characterized in that, described the 2nd subscriber equipment sends signaling message to described the 2nd base station, indicates described the 2nd subscriber equipment and sends with described predetermined level.

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